Chapter 9 Classification

Lesson Objectives

Describe phylogenetic classification, and explain how it differs from Linnaean classification.

WORKBOOK ASSIGNMENT:

No workbook pages for this chapter! Yay!

Vocabulary

binomial nomenclature

method of naming species with two names, consisting of the genus name and species name

domain

taxon in the revised Linnaean system that is larger and more inclusive than the kingdom

genus

taxon above the species in the Linnaean classification system; group of closely related species

kingdom

largest and most inclusive taxon in the original Linnaean classification system

Linnaean classification system

system of classifying organisms based on observable physical traits; consists of a hierarchy of taxa, fro the kingdom to the species

species

group of organisms that are similar enough to mate together and produce fertile offspring

taxa

a grouping of organisms in a classification system such as the Linnaean system; for example, species or genus

taxonomy

science of classifying organisms

Introduction

God created a huge variety of species. For more than 2,000 years, humans have been trying to classify the great diversity of life. The science of classifying organisms is called taxonomy. Classification is an important step in understanding the present diversity on Earth.

Linnaean Classification

All modern classification systems have their roots in the Linnaean classification system. It was developed by Swedish botanist Carolus Linnaeus in the 1700s.

Natural History Museum: Carl Linnaeus:

He tried to classify all living things that were known at his time. He grouped together organisms that shared obvious physical traits, such as number of legs or shape of leaves. For his contribution, Linnaeus is known as the “father of taxonomy.” The Linnaean system of classification consists of a hierarchy of groupings, called taxa (singular, taxon). Taxa range from the kingdom to the species (see Figure below). The kingdom is the largest and most inclusive grouping. It consists of organisms that share just a few basic similarities. Examples are the plant and animal kingdoms. The species is the smallest and most exclusive grouping. It consists of organisms that are similar enough to produce fertile offspring together. Closely related species are grouped together in a genus.

Linnaean Classification System: Classification of the Human Species. This chart shows the taxa of the Linnaean classification system. Each taxon is a subdivision of the taxon below it in the chart. For example, a species is a subdivision of a genus. The classification of humans is given in the chart as an example.

Classification of Living Things (I recommend speeding up this video to about 1.5 x speed, so that it doesn’t drag on and on – just click on the gear icon on the video and choose “speed”):

Binomial Nomenclature

Perhaps the single greatest contribution Linnaeus made to science was his method of naming species. This method, called binomial nomenclature, gives each species a unique, two-word Latin name consisting of the genus name and the species name. An example is Homo sapiens, the two-word Latin name for humans. It literally means “wise human.” This is a reference to our big brains. Why is having two names so important? It is similar to people having a first and a last name. You may know several people with the first name Michael, but adding Michael’s last name usually pins down exactly whom you mean. In the same way, having two names uniquely identifies a species.

Revisions in Linnaean Classification

Linnaeus published his classification system in the 1700s. Since then, many new species have been discovered. The biochemistry of organisms has also become known. Eventually, scientists realized that Linnaeus’s system of classification needed revision. A major change to the Linnaean system was the addition of a new taxon called the domain. A domain is a taxon that is larger and more inclusive than the kingdom. Most biologists agree there are three domains of life on Earth: Bacteria, Archaea, and Eukaryota. Both Bacteria and Archaea consist of single-celled prokaryotes. Eukaryota consists of all eukaryotes, from single-celled protists to humans. This domain includes the Animalia (animals), Plantae (plants), Fungi (fungi), and Protista (protists) kingdoms.

Lesson Summary

Classification is an important step in understanding life on Earth. All modern classification systems have their roots in the Linnaean classification system. The Linnaean system is based on similarities in obvious physical traits. It consists of a hierarchy of taxa, from the kingdom to the species. Each species is given a unique two-word Latin name. The recently added domain is a larger and more inclusive taxon than the kingdom.

Lesson Review Questions

Recall

1. What is taxonomy?

2. Define taxon and give an example.

3. What is binomial nomenclature? Why is it important?

4. What is a domain? What are the three domains of life on Earth?

Apply Concepts

5. Create a taxonomy, modeled on the Linnaean classification system, for a set of common objects, such as motor vehicles, tools, or office supplies. Identify the groupings that correspond to the different taxa in the Linnaean system..